This invention relates to a radio communication apparatus for selectively receiving a call signal and an additional or message signal succeeding the call signal. The radio communication apparatus may be a radio paging receiver, a transceiver, or the like although description will be mainly directed to the radio paging receiver.
A radio paging receiver of the type described comprises a receiving section for receiving a plurality of call signals and a plurality of message signals succeeding the call signals, respectively, as received signals. The received signals are supplied to a decoder section to be decoded. More specifically, the decoder section is for distinguishing a specific one of the call signals from other call signals that is specific to the paging receiver. When the specific call signal is distinguished from other call signals, the decoder section receives a message signal succeeding the specific call signal. The message signal is supplied to a central processing unit (CPU) to be processed and to be stored in an RAM and displayed.
In a conventional paging receiver, the receiving section is intermittently put into operation for saving an electric power supplied to the paging receiver. The decoder section and the CPU are operated by clock signals different from each other. The decoder section operates in accordance with a first clock signal having a first frequency. The CPU operates in accordance with a second clock signal which has a second frequency which is higher than the first frequency. The first and second clock signals are supplied to the decoder section and the CPU from a clock generating section which serves as an operating section.
When the receiving section is put into operation, the CPU operates in accordance with the second high speed clock signal. As a result, the receiving section has a signal to noise ratio which is influenced by noise caused by the second clock signal. Namely, it is difficult to maintain a satisfactory signal to noise ratio in the conventional radio paging receiver.